Wireless communication networks are often configured to provide a plurality of “multiple access” communication channels over which communications can be simultaneously transmitted. Often, the network is divided into a plurality of virtual “subnetworks,” or “subnets,” that transmit information over assigned communication “channels” within the network. Specific protocols are widely used to enable simultaneous multiple access, by separating the channels in time (e.g. Time Division Multiple Access, “TDMA”), in frequency (Frequency Division Multiple Access, “FDMA”) and/or by orthogonal coding (Code Division Multiple Access, “CDMA”). Nevertheless, as the demand for simultaneous multiple access increases, network contention can increase, leading to self-interference within the network.
An example is the Link 16 networking system. Link 16 is a widespread tactical wireless networking system that is used by front line land, air, and naval systems in the United States, NATO, and allied nations to allow multiple users to share situational awareness data. In particular, Link 16 is a wireless protocol based on a TDMA omnidirectional waveform which also employs FDMA and CDMA. Messages transmitted on Link 16 networks are grouped in functional areas, and allocated to “Network Participation Groups” (NPGs), also sometimes referred to simply as Participation Groups (PGs), which function as virtual networks that are distinguished according to the specific functions and purposes of the messages that they carry (e.g. network management).
According to the TDMA protocol, information is transmitted on a Link 16 network in timeslots that repeat every TDMA frame, or “epoch.” The total number of timeslots included in a Link 16 network can be divided into subsets that represent virtual subnetworks, also referred to as “subnets.” Each subnet is distinguished according to the subset of the Link 16 time slots that belongs to the subnet, as well as by the participants that share the subset of time slots. Link 16 subnets are also differentiated by their frequency-hopping patterns. Multiple subnets in a network can be “stacked” or “multinetted” by allowing time slots to be used redundantly, with the data transmitted in each net on different frequencies (FDMA) and possibly also with different coding (CDMA). Each subnet of a Link 16 network is assigned a “net number” that designates its timeslots and particular hopping pattern.
A typical link 16 network is shown in FIG. 1A. The blocks 10 in the ring 12 are time slots. Each participant 14 is provided transmit, receive, and relay time slot assignments by a network planner (not shown) prior to start of a mission. The column 16 to the right of the ring 12 illustrates the ability for Link 16 to operate on multiple nets (shown as stacked rings in the column 16). Each of the rings in the column 16 can be replaced, allowing users to form sub-networks or sub-nets allowing them to exchange data using different CDMA and FDMA codes to expand the capability of the network.
Each Link 16 participant terminal is initialized with a unique identifier, known as the Source Track Number (STN), along with time slot assignments that indicate which time slots are to be used for transmitting, receiving, and relaying. In addition to containing the starting time slot index and recurrence rate, each time slot assignment includes the NPG number for that time slot.
All Link 16 participants periodically exchange Precise Participant Location and Identification (PPLI) messages, which are generated by the terminal and provide identification, position, and status information to the Link 16 network. Details of the construction of these messages can be found in MIL-STD-6016.
With the advent of multiple message reception in a single time slot (known as Concurrent Multi-Netting (CMN) and Concurrent Contention receive (CCR)), participants in a Link 16 network are able to simultaneously receive messages from multiple transmitters in the same sub-network (CCR) as well as from transmitters in different subnetworks (CMN), thereby allowing increased use of stacked nets and subnetworks, including subnetworks that include only selected groups of nodes from the Link 16 network.
This increased use of stacked nets and subnetworks can lead to increased network contention, whereby a greater number of users transmit in the same timeslot. Although Link 16's FDMA and CDMA characteristics allow for multiple sub-networks to co-exist in close proximity, nevertheless as more participants are added to the network, self-interference can degrade the overall network performance.
What is needed, therefore, are methods for reducing self-interference in wireless network while maintaining and enhancing the ability for simultaneous multiple access.